Sarah c is right, it's a warning, from our experience some of the colours, ie blue, black ,siamese seem to be a lot more ''highly strung'' than say your pew's, silvers etc. Keep a watchful eye on them, hopefully they will settle down, they may be just sorting out the pecking order as happens when tubs are clean with no smells, and it seems common for newly paired mice too, and yes it is usually the boys that are the problem!!! and have followed up on the threat with a bite, don't let them get the better of you they can get quite stroppy :lol: :lol: